John and Jesica are planning a family, but since each has a brother who has sickle cell anemia, they are concerned that their children may develop sickle-cell disease. Neither John, Jane nor their respective parents have the disease. They consult a genetic counselor who tells them:

Correct Answer: D

Rationale: Sickle cell anemia is autosomal recessive. Both John and Jesica are likely carriers (1/2 chance each, given affected siblings and unaffected parents). Risk of an affected child is 1/4 if both are carriers, but testing is needed to confirm carrier status.

Correct Answer: B

Rationale: The Y chromosome’s SRY gene determines maleness, as seen in conditions like 47,XXY (male) vs. 45,X (female).

Correct Answer: C

Rationale: Cancer cells proliferate uncontrollably and can become immortal (e.g., HeLa cells), evading normal cell death.

Correct Answer: A

Rationale: The Philadelphia chromosome (t(9;22)) creates the BCR-ABL fusion gene in chronic myeloid leukemia.

Correct Answer: D

Rationale: A germline mutation is present in all cells of an individual, inherited from a gamete.